1. Field of the Invention
The present invention relates mainly to a stereo microphone apparatus and particularly to a stereo microphone apparatus for binaural sound pickup used in dummy head recording or the like.
2. Description of the Prior Art
Acoustic reproducing systems have hitherto, been variously changed from a monaural system to a stereo system, to a 4-channel system and even further to a multi-channel system for the purpose of providing more faithful acoustic reproduction of the original sound field. To attain this end, not only one microphone but also a number of microphones have been used to establish a multi-microphone system in which the outputs thereof are properly mixed and transmitted through a number of channels.
In these systems, however, the original sound field has to be reproduced in, for example, the listening room of a listener, and this listening room must be wide to some extent. It is noted, on the other hand, that based upon the fact that we generally use our ears to recognize the direction from which sound signals arrive and the distance from the sound sources whether they are in front or back, right or left, or upper or lower directions, it is conceived that the necessary and sufficient information transmission can be attained by producing acoustic information signals which correspond to what the two ears of a listener in the original sound field would have actually listened to. According to this idea, only a transmission system is required by which the acoustic information provided in the eardrums of the listener in the original sound field is again produced in the eardrums of the listener in the reproducing room. In this case, the reproducing room can be selected quite freely. Besides, it is sufficient if the transmission system has two channels. Such a two-channel system is very low in cost and the reproduction of acoustic information, as good as the conventional multi-channel system, becomes possible.
It is understood that experiments of a binaural stereo system along the aforesaid lines were carried out in the year 1930 by the Bell Telephone Laboratories. In this case, satisfactory reliable results were achieved on account of the performance of sound pickup microphones, reproducing headphones and the like. The term "pinna" as used herein, is the largely cartilogenous projecting portion of the external ear.
Accordingly, there has been proposed a microphone apparatus suitable for sound pickup to satisfy the above condition. A prior art stereo microphone apparatus of this kind has a dummy head normally made of silicon rubber or the like and has a pair of symmetric microphone units, each mounted at the position of the inlet to auditory canal of a dummy head or eardrum thereof. This microphone apparatus is designed so that a condition from a sound source to the inlet of the microphone may become close to the condition of actual human ears. However, since the size of the microphone apparatus is fixed and constant, if there is a difference between the shape and size of the dummy head and those of a listener's head, it is not always possible to achieve good results. In addition, microphone apparatus of the aforesaid type is high in cost, and it is also large in size and heavy in weight, with the result that transportation of the same is inconvenient.
In order to eliminate the aforesaid drawbacks, it has been proposed that the following microphone apparatus be used; namely, that the microphone apparatus comprise an arc-shaped resilient pipe, a pair of microphone units attached to the opposite ends of the pipe, and supporting members on which are mounted the pair of microphone units. Each of the supporting members serves to cause the sound inlet of microphone to be positioned near the orifice of the auditory canal. An output cord is led out from the center of the resilient pipe, and the microphone apparatus is formed in the shape of a stethoscope.
This microphone apparatus is normally used in such a manner that it is directly mounted on the human ears or located on a dummy head having no microphone. This microphone apparatus greatly improves the above mentioned defects, but still has the drawbacks such that it easily picks up a wind noise and a code contact noise and is low in stability when it is mounted on human ears.